A piezoelectric transducer may be used to generate full audio band acoustic signals by coupling the piezoelectric transducer to a suitable surface that acts as a loudspeaker. Accordingly, consumer electronic products with large display screens such as smartphones, tablets, personal computers, and televisions may benefit from adopting piezoelectric transducers as audio transducers that mechanically drive a screen. The large screen area may move a large mass of air thereby increasing loudness and bass response. As the piezoelectric transducer may be mounted behind the screen, there may be no requirement for an opening or acoustic port in the screen or body of the consumer electronic product, as is the case with traditional approaches, enabling more surface to be dedicated to display and simplifying waterproof device designs.
Piezoelectric transducers present a mostly capacitive impedance at audio frequencies (e.g., 20 Hz-20 KHz) with a small resistive component in series with the capacitive impedance. At higher audio frequencies, a reduced impedance may cause high currents to flow which, in turn, may cause self-heating in a piezoelectric transducer. The self-heating may be a function of an electrical impedance of the piezoelectric transducer, the frequency and voltage of the electrical signal driving the piezoelectric transducer, mechanical mounting of the piezoelectric transducer and the resultant force induced, and a thermal resistance of the enclosure around the piezoelectric transducer. The temperature of a piezoelectric transducer is therefore difficult to predict for a given mounting, enclosure, and drive signal.
Below a temperature known as the Curie temperature, characteristics of a piezoelectric material, such as the charge constant, voltage constant, and permittivity all vary with temperature which may introduce dynamic non-linearity into a transfer function of the piezoelectric transducer. Above the Curie temperature, piezoelectric material may depolarize, potentially causing mechanical and acoustic properties to be permanently degraded or lost.
It is therefore desirable to measure and control the self-heating within a piezoelectric transducer when driving audio signals. While existing temperature sensors may permit sensing a temperature proximate to, but external to, a piezoelectric transducer, existing approaches are not effective in measuring temperatures internal to a piezoelectric transducer.